Wireless base station and wireless communication method

Abstract

A transmission path state estimation unit estimates a state of a transmission path to a wireless terminal based on a DRS (Demodulation Reference Signal) included in uplink user data received from the wireless terminal when a re-sending request is received after transmission of an SRS is stopped. A transmission unit forms directivity of a plurality of antennas based on the estimated state of the transmission path and transmits downlink user data.

The invention claimed is: 
     
       1. A wireless base station, comprising:
 a resource determiner that determines at least a part within any downlink subframe as a first resource for transmitting downlink user data to a wireless terminal and determines at least a part of an uplink part within a switch subframe or a part of an uplink subframe as a second resource for said wireless terminal to periodically transmit a sounding reference signal; 
 a resource notifier that notifies said wireless terminal of said second resource; 
 a transmission path state estimator that estimates a state of a transmission path to said wireless terminal based on a reference signal included in uplink user data received from said wireless terminal when a re-sending request is received after transmission of said sounding reference signal is stopped; and 
 a transmitter that forms directivity of a plurality of antennas based on the estimated state of the transmission path and transmits said downlink user data through said first resource. 
 
     
     
       2. The wireless base station according to  claim 1 , wherein said transmission path state estimator estimates a state of the transmission path to said wireless terminal based on a received, most recent sounding reference signal in a transmission section of said sounding reference signal. 
     
     
       3. The wireless base station according to  claim 1 , wherein when said re-sending request is received, said resource determiner determines at least a part within any uplink subframe as a third resource for said wireless terminal to transmit uplink user data including said reference signal, and said resource notifier notifies said wireless terminal of determined said third resource. 
     
     
       4. The wireless base station according to  claim 3 , wherein
 said wireless base station is a wireless base station in a communication system adapted to an LTE (Long Term Evolution) scheme, and 
 said resource determiner determines said first resource, said second resource, and said third resource in accordance with a frame configuration of which Uplink-downlink configuration is “1”. 
 
     
     
       5. The wireless base station according to  claim 1 , wherein
 when said re-sending request is received after transmission of said sounding reference signal is stopped and when a cumulative total of received said re-sending requests is smaller than a first value, said transmission path state estimator estimates a state of the transmission path to said wireless terminal based on last received said sounding reference signal, and when a cumulative total of received said re-sending requests is equal to or greater than said first value, said transmission path state estimator estimates a state of the transmission path to said wireless terminal based on the reference signal included in the uplink user data received from said wireless terminal. 
 
     
     
       6. The wireless base station according to  claim 5 , further comprising a terminal speed controller which controls a moving speed of said wireless terminal, wherein
 when a speed of said wireless terminal is equal to or greater than a prescribed value, said transmission path state estimator estimates a state of said transmission path with said first value being decreased as compared with a case where a speed of said wireless terminal is smaller than said prescribed value. 
 
     
     
       7. The wireless base station according to  claim 1 , wherein
 said wireless base station is a wireless base station in a communication system adapted to an LTE (Long Term Evolution) scheme, and 
 said uplink part is an UpPTS (Uplink Pilot Timeslot). 
 
     
     
       8. A wireless base station, comprising:
 a resource determiner that determines at least a part within any downlink subframe as a first resource that transmits downlink user data to a wireless terminal and determines at least a part of an uplink part within a switch subframe or a part of an uplink subframe as a second resource for said wireless terminal to periodically transmit a sounding reference signal; 
 a resource notifier that notifies said wireless terminal of determined said second resource; 
 a transmission path state estimator which estimates a state of a transmission path to said wireless terminal based on a received, most recent sounding reference signal in a transmission section of said sounding reference signal, estimates a state of a transmission path to said wireless terminal based on last received said sounding reference signal when a re-sending request is received after transmission of said sounding reference signal is stopped and when a cumulative total of received said re-sending requests is smaller than a first value, and estimates a state of a transmission path to said wireless terminal based on a reference signal included in uplink user data received from said wireless terminal when a cumulative total of received said re-sending requests is equal to or greater than said first value; and 
 a transmitter that forms directivity of a plurality of antennas based on estimated said state of the transmission path and transmits said downlink user data through said first resource. 
 
     
     
       9. The wireless base station according to  claim 8 , wherein
 when said re-sending request is received and when the cumulative total of said received re-sending requests is equal to or great than said first value, said resource determiner determines at least a part within any uplink subframe as a third resource for said wireless terminal to transmit uplink user data including said reference signal, and 
 said resource notifier notifies said wireless terminal of determined said third resource. 
 
     
     
       10. The wireless base station according to  claim 9 , wherein
 said wireless base station is a wireless base station in a communication system adapted to an LTE (Long Term Evolution) scheme, and 
 said resource determiner determines said first resource, said second resource, and said third resource in accordance with a frame configuration of which Uplink-downlink configuration is “1”. 
 
     
     
       11. The wireless base station according to  claim 8 , further comprising a terminal speed controller which controls a moving speed of said wireless terminal, wherein
 when a speed of said wireless terminal is equal to or greater than a prescribed value, said transmission path state estimator estimates a state of said transmission path with said first value being decreased as compared with a case where a speed of said wireless terminal is smaller than said prescribed value. 
 
     
     
       12. The wireless base station according to  claim 8 , wherein
 said wireless base station is a wireless base station in a communication system adapted to an LTE (Long Term Evolution) scheme, and 
 said uplink part is an UpPTS (Uplink Pilot Timeslot). 
 
     
     
       13. A wireless communication method, comprising the steps of:
 determining at least a part within any downlink subframe as a first resource for transmitting downlink user data to a wireless terminal and determining at least a part of an uplink part within a switch subframe or a part of an uplink subframe as a second resource for said wireless terminal to periodically transmit a sounding reference signal; 
 notifying said wireless terminal of determined said second resource; 
 estimating a state of a transmission path to said wireless terminal based on a reference signal included in uplink user data received from said wireless terminal when a re-sending request is received after transmission of said sounding reference signal is stopped; and 
 forming directivity of a plurality of antennas based on estimated said state of the transmission path and transmitting said downlink user data through said first resource. 
 
     
     
       14. A wireless communication method, comprising the steps of:
 determining at least a part within any downlink subframe as a first resource for transmitting downlink user data to a wireless terminal and determining at least a part of an uplink part within a switch subframe or a part of an uplink subframe as a second resource for said wireless terminal to periodically transmit a sounding reference signal; 
 notifying said wireless terminal of determined said second resource; 
 estimating a state of a transmission path to said wireless terminal based on a received, most recent sounding reference signal in a transmission section of said sounding reference signal; 
 estimating a state of a transmission path to said wireless terminal based on last received said sounding reference signal when a re-sending request is received after transmission of said sounding reference signal is stopped and when a cumulative total of received said re-sending requests is smaller than a first value; 
 estimating a state of a transmission path to said wireless terminal based on a reference signal included in uplink user data received from said wireless terminal when a re-sending request is received after transmission of said sounding reference signal is stopped and when a cumulative total of received said re-sending requests is equal to or greater than said first value; and 
 forming directivity of a plurality of antennas based on estimated said state of the transmission path and transmitting said downlink user data through said first resource.